Problem with styling select (dropdown) comboboxes

I have a simple membership form which is set up with the Forminator (free) Design Style set to None so that the styling can be set by my theme – a simple child theme of GeneratePress where the only other customisation is to set the site text font and minor formatting of the Navigation menu.

I can set the styling of all elements except the select comboboxes, using the CSS –

.forminator-button-submit {
    border-radius: 16px;
    background: green;
}
.forminator-label {
    display: inline-block;
    width: 200px;
    height: 30px;
    font-weight: bold;
}
.forminator-input,
.forminator-input[type=text],
.forminator-input[type=email] {
    display: inline-block;
    width: 400px;
    height: 30px;
    padding: 5px;
    border: 1px solid black;
    background-color: #f0ffff;
    margin-right: 5px;
}

I have tried all combinations of -input, -select, -dropdown, and [type=select] with .forminator but failed to change the select styling.

Can you provide me with the correct CSS syntax to style the select elements ?

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